You don't have to bring your own flashlight to take a tour of the cities that humans have built underground. Just lean back and let these videos unlock all of their subterranean secrets.

Derinkuyu, Turkey, built in the 7th or 8th century by Christians hiding from persecution, could house up to 20,000 people.

The Burlington Bunker in Corsham, Wiltshire, England, built as an emergency relocations site for the British government in the event of a nuclear attack during the 1950s

The Beijing Underground City, a complex of tunnels covering an area of 33 square mile, built as a bomb shelter in the 1970s, with factories, a roller skating rink, schools, restaurants, oil and grain warehouses, and homes, of course.

Barry Troglodyte village in Rhone valley, France, with houses inhabited continously from the Neolithic era to the early 20th century

A small secret city under Leavenworth, Kansas from the late 19th century

Moose Jaw, Saskatchewan, Canada. Its network of tunnels were full with factories, shops, speakeasies, once housed Chinese immigrants and were allegedly used for smuggling by the legendary Al Capone.

The mysterious tunnels of Erdstall, Germany, connecting the farmhouses, churches and the cemetery, rediscovered only a few years ago.